The invention relates to engine intake resonators, and more particularly to a space-efficient and manufacturing-efficient multi-frequency resonator.
For a multiple-cylinder internal combustion engine operating in a specific RPM (revolutions per minute) range, the dominant firing frequencies of the induction noise can vary substantially. Conventional side-branch resonators used in the induction system such as Helmholtz and quarter-wavelength resonators are tuned to specific frequencies and are only effective within narrow operating ranges. The resonators cancel the induction noise at the predetermined resonant frequency. Typical intake resonators occupy a large volume or lengthy dimension in packaging space and are generally restricted to higher frequency applications by such volume and length.
The present invention overcomes the noted space requirements, and also affords manufacturing efficiencies, in providing a one-piece unit of multiple quarter-wavelength resonators used to attenuate multiple dominant frequencies of the induction noise. The targeted noise can be either the fundamental firing frequency and its subsequent harmonics at a fixed engine operating RPM, or the fundamental firing frequencies at various fixed engine operating RPMs.
In the preferred embodiment, the invention provides a one-piece unit of multiple quarter-wavelength resonators designed to attenuate selective dominant frequencies of the induction noise. A plastic intake resonator is molded to conform to available packaging space, and can be incorporated into the existing air cleaner housing, engine cover, bottom pan, door panel of the engine or the equipment, etc. The invention enables the use of different materials and molding processes to manufacture the resonators, including injection molding, blow molding, and rotational molding. The invention enables the use of twin-sheet forming, a process known and familiar to those in the art and manufacturing-efficient, to afford a low cost manufacturing process for a plastic intake resonator.
The resonant frequency of a quarter-wavelength resonator is determined by its length, and a single resonator is capable of reducing the tonal frequency noise by 5 to 15 dB. In order to target several frequencies simultaneously, a one-piece unit of multiple quarter-wavelength resonator segments can be formed by folding the side-branch resonator tubes into two or more segments. The cross-sectional shape of the tube can be varied as long as its cross-sectional area over the length remains constant, in the preferred embodiment. The end of each tube is capped and preferably remains airtight for the best acoustical performance.
The invention enables the noted use of twin-sheet forming as a molding technique for making the quarter-wavelength resonators. This process involves the forming of two separate heated plastic sheets of material into separate tools while fusing them together under pressure to make a part with hollow sections. The heated flat sheet of thermoplastic is shaped to form two clamshell-like mating parts. Metal inserts or discs can be molded into the part to adjust the length of the quarter-wavelength tube required for acoustic tuning. The process yields superior bonding as compared to other post-forming methods, and is accomplished during a single machine cycle. Additional features such as taps and bolt holes for fastening can be included in the molded part.